new spring boxes from Mercedes are around £150 each!...(pause while i get back on my seat)
but according to the nice chap i spoke to, most mercedes seats are interchangeable, unless they are orthopedic seats. he wasn't very precise when i questioned further but certainly encouragement enough, if £300 wasn't, to check out some second hand seats.
i'll let you know how i get on, when i get to the bottom of it!
sorry about that, i couldn't resist it..